Adding An Economic Component to the University of Nebraska Nitrogen Corn Recommendation Procedures.

The University of Nebraska nitrogen recommendation algorithm has developed since its initial formulation in the 1970s and with a major revision in the 1990s based on additional research in the 1980s. The algorithm has been promoted through use by Nebraska’s Natural Resources Districts where groundwater nitrate is commonly greater than 10 mg L^-1.  The algorithm considered linear effects of soil nitrate concentration, soil organic matter, and yield goal with credits for previous crop and other known nitrogen sources such as manure and irrigation water N. When crop prices and nitrogen prices started to fluctuate in the mid 2000s, the Nebraska Soil Fertility Team decided to incorporate the price of nitrogen and the value of corn into the recommendation procedure.  Between 2002 and 2004 the team conducted 34 N rate experiments in high yielding, irrigated environments with the intent of refining the algorithm. The experiments verified the algorithm and the results were used to construct a curvilinear response function between N rate and yield. From that function the economic implications of a change in N rate were calculated and an adjustment factor was developed based on the corn:nitrogen ratio (in English units). To facilitate use of this recommendation procedure, an Excel spreadsheet, a slide rule, and an on-line soil test program (soiltest.unl.edu) were developed to calculate a nitrogen recommendation based on inputs supplied by the user. The revised algorithm and tools have been promoted through diverse Extension activities.